1. Field of the Invention
The present invention relates to an optical element having an optical functional layer obtained by polymerization of a polymerizable liquid crystal material, wherein the above-mentioned optical functional layer has a high hardness.
2. Description of the Related Art
Conventionally, an optical element such as a retardation film and a circularly polarized light control optical element, used for an image display apparatus or the like, can be used in a state assembled in an image display apparatus such as a liquid crystal display apparatus. In production of such an image display apparatus, another member can be provided by superimposing on the above-mentioned optical element. For example, in the case the optical element is a retardation film used for a liquid crystal display apparatus, or the like, a spacer (column) is formed on the retardation film for making the liquid crystal layer gap even.
At the time, in the case the hardness of the optical element itself is low, the optical element may be distorted at the time of forming the above-mentioned spacer, or the like so that the accuracy as the optical device cannot be maintained. Moreover, in the case the optical element itself is distorted by application of a slight force, the optical characteristics of the optical element are fluctuated, and thus it can be problematic.
In contrast, recently, an optical element obtained by polymerization of a polymerizable liquid crystal material has been proposed (for example, Japanese Patent Application Laid-Open (JP-A) No.2001-100045, No.10-508882, or the like). According to the optical element, since the characteristics of the liquid crystal can be used as a film by solidification by polymerization, development to various applications is expected.
However, since maintenance of the hardness of the optical element, obtained by polymerization of a polymerizable liquid crystal material, itself at a high level has not been proposed conventionally, the problems of the above-mentioned accuracy as the optical device and the fluctuation of the optical characteristics of the optical element itself have not been solved.
The object of the present invention is to provide an optical element capable of maintaining the accuracy in the case of used in an optical device such as an image display apparatus without generation of the fluctuation of the optical characteristics at the time of being assembled in an optical device even in the case a load is applied.
In order to achieve the above-mentioned object, the present invention provides an optical element comprising a supporting member and an optical functional layer of a polymerizable liquid crystal material hardened on the supporting member with a predetermined liquid crystal regularity; wherein the optical functional layer has a 17 or more Vickers hardness value; and an optical element comprising a supporting member and an optical functional layer of a polymerizable liquid crystal material hardened on the supporting member with a predetermined liquid crystal regularity; wherein the optical functional layer has a B or more pencil hardness value.
According to the present invention, since the optical functional layer has a hardness in the above-mentioned range, for example, in the case it is assembled in an optical device or the like, a problem such as deterioration of accuracy, due to deformation at the time of providing another member thereon, dose not occur. Moreover, even in the case for example a columnar spacer, for maintaining the gap of the liquid crystal layer of the liquid crystal display apparatus even, is formed on the optical element of the present invention so as to apply a partial force, since the above-mentioned high hardness is provided, locally change of the film thickness can hardly be generated so that the risk of generating fluctuation in terms of the optical characteristics due to influence of the film thickness of the optical element of the present invention can be lowered.
In the present invention, the above-mentioned supporting member may be a base material having the alignment ability. An optical element of the present invention is obtained by polymerizing a polymerizable liquid crystal material in a state having a regular liquid crystal phase. Therefore, in order to obtain a regular liquid crystal phase, it should be formed on a base material having the alignment ability, and thus it is advantageous in terms of the cost to use as it is as the optical element on the base material having the alignment ability.
In the present invention, the above-mentioned supporting member may be a base material to be transferred and the above-mentioned base material to be transferred may be a transparent substrate. In the case a specific function is necessary on the base material, or the like, an optical functional layer can be formed on the material to be transferred in a transfer step. It is preferable, in terms of the function as the optical element, to use a transparent substance as the material to be transferred at the time.
In the present invention, it is preferable that the above-mentioned polymerizable liquid crystal material is a polymerizable liquid crystal monomer, the above-mentioned predetermined liquid crystal regularity is a nematic regularity or a smectic regularity, and the above-mentioned optical functional layer is a retardation layer. In the case such an optical element having a retardation layer is used, the hardness of the retardation layer is important in terms of the accuracy, or the like.
Moreover, in the present invention, it is preferable that the above-mentioned polymerizable liquid crystal material is a polymerizable liquid crystal monomer and a polymerizable chiral agent, the predetermined liquid crystal regularity is a choresteric regularity, and the above-mentioned optical functional layer is a choresteric layer. Since such a choresteric layer, that is, a layer solidified in the state having a choresteric regularity, functions as the circularly polarized light control layer, the hardness thereof is important in terms of the accuracy also in this case.
In the present invention, it is preferable that a protection layer is formed on the above-mentioned optical functional layer. Since the hardness on the protection layer can be made higher if the optical functional layer hardness is within the above-mentioned range, as it is as the optical element even in the case the protection layer is provided, it is preferable in terms of the accuracy in the case of use in an optical device.
The present invention provides a manufacturing method for an optical element comprising a step of preparing a base material having the alignment ability; a step of forming a liquid crystal layer having a predetermined liquid crystal regularity by laminating a liquid crystal layer forming composition, comprising at least a polymerizable liquid crystal material on the base material a step of applying a thermal treatment to the liquid crystal layer at the N-I transition point or lower; a step of forming an optical functional layer by irradiating an active radioactive ray to the liquid crystal layer at a room temperature or while heating so as to provide an optical functional layer; and a step of re-hardening process by heating the optical functional layer at a temperature in a range of 150xc2x0 C. to 260xc2x0 C. for executing a re-hardening process.
According to the present invention, since the re-hardening process is execute data predetermined temperature for the optical functional layer, obtained by polymerizing a polymerizable liquid crystal material, as mentioned, the hardness of the optical functional layer can be improved, and then, the accuracy can be improved when used in an optical device, or the like.
In the present invention, the above-mentioned polymerizable liquid crystal material may be a polymerizable monomer, and the predetermined liquid crystal regularity may be a nematic regularity or a smectic regularity. Such an optical functional layer serves as a retardation layer so that it can be used for various applications requiring a retardation function, such as a xcex/4 retardation plate.
Moreover, in the present invention, the above-mentioned polymerizable liquid crystal material may be a polymerizable monomer and a polymerizable chiral agent, and the predetermined liquid crystal regularity may be a choresteric regularity. Such an optical functional layer may be used as a circularly polarized light control layer and a retardation element for various applications such as a color filter.
In the present invention, it is preferable that a photo polymerization initiating agent is contained in the above-mentioned liquid crystal layer forming composition. As mentioned, since the photo polymerization initiating agent is contained, the hardness can be raised effectively in the re-hardening process step.
In the present invention, it is preferable that the above-mentioned re-hardening process step is carried out under a non-oxygen atmosphere. Under the non-oxygen atmosphere, the hardness can be raised effectively. Here, the non-oxygen atmosphere is preferably a nitrogen atmosphere as mentioned in claim 13. It is the method most commonly used for having a non-oxygen atmosphere and it is also advantageous in terms of the cost.
In the present invention, it is preferable that the above-mentioned liquid crystal layer forming composition is a liquid crystal layer forming coating solution using a solvent. Such a method using a liquid crystal layer forming coating solution can easily be carried out in the step compared with the other methods such as a method of forming a dry film and a method of melting and coating.
In the present invention, it is preferable that the heating time for the above-mentioned re-hardening process is within a range of 1 minute to 240 minutes. It is preferable to heat within the above-mentioned range of timer, from the viewpoint of raising the hardness.
In the present invention, it is preferable that a transfer step for transferring the above-mentioned optical functional layer, formed on the base material having the alignment ability, onto the material to be transferred is provided after the optical functional layer forming step. For example in the case the optical functional layer is necessary on the material to be transferred having another function, or the like, the transfer step for transferring the optical functional layer on the material to be transferred can be carried out as well. In this case, by executing the above-mentioned re-hardening process step after the transfer, the hardness of the optical functional layer on the material to be transferred can be raised.
In the present invention, it is preferable that a protection layer forming step is executed after the above-mentioned optical functional layer forming step, and then a re-hardening process step is executed. By executing the re-hardening process step together with the protection layer, the hardness of the optical functional layer and the protection layer can be raised so that the accuracy can be improved at the time of use in an optical device.
According to the present invention, since the hardness of the optical functional layer is a high hardness in a predetermined range, even in the case it is assembled in an optical device, or the like, generation of a problem such as the accuracy deterioration due to deformation at the time of providing another member thereon, or the like can be prevented. Moreover, also in the case a columnar spacer is formed on the optical element of the present invention for example for evenly maintaining a gap of the liquid crystal layer of a liquid crystal display apparatus, so as to locally apply a force, since the hardness is provided as mentioned above, the local change of the film thickness can hardly be generated, and thus an effect of reducing the risk of the optical characteristic fluctuation of the optical element of the present invention can be achieved.